1. Field of the Invention
The present invention generally relates to processing multimedia information, and in particular to an apparatus and method for encoding and/or decoding a moving picture using digital watermarking techniques.
2. Description of the Related Art
In order to communicate images which have a real and natural appearance, a number of three-dimensional image communication techniques have been developed. In next-generation image processing, a three-dimensional image processing method which uses a binocular image (e.g., an image at which depth can be perceived by recognizing an object with binocular of a human being) has been a matter of grave concern. Because today most images are color moving pictures, transmission rate on a communication channel and processing speed are very important considerations. To enhance transmission rate and processing speed, increasing image information quantity required to obtain the so-called cubic effect has become of critical interest. Accordingly, it is urgent to develop a method for compressing image information easily and efficiently while maintaining picture quality of a cubic image.
FIGS. 1A and 1B illustrate a related-art method for obtaining a three-dimensional moving picture. Left and right eyes of a human being show two-dimensional images which are different from each other. When the two images are transmitted to the brain through the retina, the brain accurately fuses them into one image. Accordingly, depth and reality of the original three-dimensional image can be reproduced. Herein, a three-dimensional moving picture means an image obtained using plural cameras taking into consideration the visual characteristics of a human being.
FIG. 1A shows a related-art method for obtaining a three-dimensional moving picture (stereo moving picture) of one viewpoint. Pictures 5, 7 respectively photographed by cameras 1, 3 correspond to two eyes of a human being. These pictures are fused to produce a moving picture (stereo moving picture) having one viewpoint. Herein, viewpoint means a point at which depth (or cubic effect) is perceived through the two pictures 5, 7.
FIG. 1B shows a related-art method for obtaining a three-dimensional moving picture having multi viewpoints. In order to improve depth and reality, pictures 21-24 photographed by plural cameras 11-14 are fused to produce a moving picture having multiple viewpoints.
In encoding a three-dimensional moving picture having multiple viewpoints, the quantity of data produced or required is directly proportional to the number of viewpoints, e.g., unlike two-dimensional moving picture encoding the quantity of data increases with increasing numbers of viewpoints. In order to reduce the vast quantity of data that is involved, the related-art moving picture encoding apparatus performs disparity estimation to eliminate overlap between the viewpoints.
In encoding a two-dimensional moving picture, disparity estimation is used for eliminating overlap between picture frames on a temporal axis. This technique is applied for viewpoints of a three-dimensional moving picture. Accordingly, disparity estimation is a technique for searching for overlap between viewpoints in a three-dimensional moving picture. For example, in a stereo moving picture, disparity estimation means searching a block of a right image most similar to a block of a left image.
Motion estimation involves calculating a motion vector by performing motion estimation between two picture frames, performing motion compensation according to the motion vector, eliminating overlap between picture frames on the same temporal axis, and transmitting a difference between the motion-compensated previous frame and a present frame.
FIG. 2 shows a method for estimating disparity and motion of a stereo moving picture, which is taken as an example of a general three-dimensional moving picture. General moving pictures are processed in picture units involving an I picture (intra picture), a P picture (predictive picture), and a B picture (bidirectionally predictive picture). The I picture is an intra-encoded picture, the P picture is a picture forwardly predicted based on the I picture, and the B picture is embedded between the I picture and P picture. More specifically, the B picture is a picture forwardly predicted from the I picture and backwardly predicted from the P picture.
In a general stereo moving picture, a left sequence is moving picture-encoded using general motion estimation and a right sequence is moving picture-encoded using a vector value and a difference picture obtained through disparity estimation.
FIG. 3 is a block diagram showing a general stereo moving picture encoding apparatus. This apparatus includes a first motion estimator 30, a second motion estimator 32, a disparity estimator 34, a motion compensated encoder 36, and motion/disparity compensated encoder 38. The first motion estimator performs motion estimation using an input left sequence and outputs a motion vector 31 relating to a left sequence frame. The second motion estimator performs motion estimation using a right sequence and outputs a motion vector 41 relating to right sequence frame. The disparity estimator performs disparity estimation between the left sequence frame of the first motion estimator and the right sequence frame of the second motion estimator. The motion compensated encoder encodes the left sequence frame using the motion vector output from the first motion estimator and outputs left sequence encoded data 43. The motion/disparity compensated encoder encodes the right sequence frame using motion vector 41 and disparity vector 42 and outputs an encoded right sequence data 44.
Operation of the general stereo moving picture encoding apparatus will now be described. The first motion estimator 30 estimates motion about the left sequence and outputs a motion vector. In addition, the first motion estimator outputs a difference picture between the picture Cleft picture) restored by the motion vector and the original picture (original left picture). The motion compensated encoder 36 outputs the left sequence encoded data 43 by encoding the left sequence frame using the motion vector and the difference picture (difference picture in the left sequence).
Like the first motion estimator, the second motion estimator 32 performs motion estimation for the left sequence and outputs a difference picture (difference picture in the right sequence) with the motion vector 41. The disparity estimator 34 outputs the disparity vector 42 by finding redundancy between the left picture and right picture. The motion/disparity compensated encoder 38 encodes the right sequence frame using the motion vector 41, the difference picture (difference picture in the right sequence), and the disparity vector 42.
The general stereo moving picture encoding apparatus thus receives both the left sequence encoded data 43 output from the motion compensated encoder 36 and the right sequence encoded data 44 output from the motion/disparity compensated encoder 38. Accordingly, the left sequence encoded data 43 and the right sequence encoded data 44 are sequentially received.
Unlike the left sequence encoded data 43, the right sequence encoded data 44 is data obtained by encoding the motion vector 41 for the right sequence, the difference picture (difference picture in the right sequence) and the disparity vector 42. The left sequence encoded data, the motion vector of the right picture, the difference picture, and the estimated disparity vector are transmitted after estimating disparity between the left and right pictures.
A general stereo moving picture decoding apparatus receives the left sequence encoded data, the motion vector of the right sequence, the difference picture and the disparity vector, restores the left picture using the left sequence encoded data, and the right picture is then compensated and restored using the restored left picture information, the motion vector and the difference picture of the right picture and the disparity vector.
However, in the general stereo moving picture encoding apparatus, because both the left sequence encoded data and the right sequence encoded data (the motion vector and the difference picture of the right picture, and the disparity vector) are used, the quantity of data to be transmitted is increased more than that of the related-art secondary moving picture encoder. Consequently, data cannot be smoothly processed with the transmission rate of a conventional transmission channel and processing speed. In addition, by using multiple viewpoint moving picture, data quantity is increased even more.